From: Bob Nelson (nelsnjr@cox.net)
Date: Wed Sep 07 2005 - 23:19:26 GMT-3
Hello All:
I want to make sure I am clear on the preempt and track for HSRP.
Here is an example from the DocCD. My questions follow the example
In the following example, the tracking process is configured to track the IP
routing capability of serial interface 1/0. HSRP on Ethernet interface 0/0
then registers with the tracking process to be informed of any changes to
the IP routing state of serial interface 1/0. If the IP state on Serial
interface 1/0 goes down, then the priority of the HSRP group is reduced by
10.
If both serial interfaces are operational, then Router A will be the HSRP
active router because it has the higher priority.
However, if IP routing on serial interface 1/0 in Router A fails, then the
HSRP group priority will be reduced and Router B will take over as the
active router, thus maintaining a default virtual gateway service to hosts
on the 10.1.0.0 subnet.
Router A Configuration
track 100 interface serial1/0 ip routing
!
interface Ethernet0/0
ip address 10.1.0.21 255.255.0.0
standby 1 ip 10.1.0.1
standby 1 priority 105
standby 1 track 100 decrement 10
Router B Configuration
track 100 interface serial1/0 ip routing
!
interface Ethernet0/0
ip address 10.1.0.22 255.255.0.0
standby 1 ip 10.1.0.1
standby 1 priority 100
standby 1 track 100 decrement 10
1. "If both serial interfaces are operational, then Router A will be the
HSRP active router because it has the higher priority."
Is this necessarily true. Does it not depend on which interface was
brought up first?. Without preempt, A will not become active if it is
brought up second, correct?
Without the preempt command on Router A, it will not take over just by
virtue of the higher priority.
2. "if IP routing on serial interface 1/0 in Router A fails, then the HSRP
group priority will be reduced and Router B will take over as the active
router"
Again, just because the priority on A (assuming it is the active) drops
below router B's priority, does not mean it will take over as active,
without B having preempt configured. Additionally, if B is configured
to preempt A when Serial 1/0 goes down on router A, so it become the active,
A must also have preempt configured to resume its active role when the
serial comes up.
Is this correct and they just did not put the preempt statements for
brevity(confuse me) or am I missing the concept.
Thanks for the help. Sorry for the length, wanted to be complete
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